(1) A multicopy plasmid vector carrying the glnD gene (structural gene for uridylyltrasferase-uridylyl-removing enzyme) was constructed by cloning the EcoRl generated fragment of the plasmid JA200/PLC 38-39. This strain overproduced UT.UR by 25-30-fold. (2) A large quantity of PII protein was purified from an overproducing strain using simplified procedures. X-ray crystallographic and UV spectral studies on PII were pursued. A tryptic undecapeptide containing covalently bound UMP was isolated and the amino acid sequence of this peptide was established. In addition, the properties of phosphotyrosyl PII generated by treating PII(UMP)4 with micrococcal nuclease were studied. (3) A continous fluorometric assay for deadenylylation reaction was developed. (4). MOnoclonal antibodies specific to various antigenic determinants of E. coli glutamine synthetase were prepared. The hybridoma clones were isolated by the fusion of myeloma cells and spleen cells derived from mice immunized with glutamine synthetase of AMP attached to bovine serum albumin.